![\"Reconstruction](\"https:\/\/cdn.sci.news\/images\/enlarge13\/image_14677e-Jiangchuan-Biota.jpg\")
<\/a><\/p>\nReconstruction of the Jiangchuan Biota. Image credit: Xiaodong Wang.<\/p>\n
The burst of animal diversification spanning the transition from the Ediacaran to the Cambrian periods stands as one of the most consequential turning points in Earth\u2019s history.<\/p>\n
Yet the fossil record offers only a fragmented view of that transformation: Ediacaran communities bear little resemblance to those of the Cambrian, leaving the pivotal moment when major animal groups emerged frustratingly out of reach.<\/p>\n
\u201cOur discovery closes a major gap in the earliest phases of animal diversification,\u201d said Dr. Gaorong Li, a researcher at Oxford University.<\/p>\n
\u201cFor the first time, we demonstrate that many complex animals, normally only found in the Cambrian, were present in the Ediacaran period, meaning that they evolved much earlier than previously demonstrated by fossil evidence.\u201d<\/p>\n
In the study, Dr. Li and colleagues examined more than 700 specimens from a recently-discovered fossil site in Yunnan, southwest China.<\/p>\n
The fossil assemblage is between 554 and 539 million years old and is part of the Jiangchuan Biota.<\/p>\n
Unlike most Ediacaran fossil sites, which preserve organisms mainly as impressions on sandstone surfaces, these fossils are preserved as carbonaceous films, a mode of preservation more typical of famous Cambrian sites such as the Burgess Shale in Canada.<\/p>\n
\u201cThis discovery is extremely exciting because it reveals a transitional community: the weird world of the Ediacaran giving way to the Cambrian, the following time period where the animals are much easier to place in groups that are alive today,\u201d said Oxford University\u2019s Dr. Luke Parry.<\/p>\n
\u201cWhen we first saw these specimens, it was clear that this was something totally unique and unexpected.\u201d<\/p>\n
The assemblage contains the oldest known relatives of deuterostomes, the broader group that today includes vertebrates such as humans and fish.<\/p>\n
Among the specimens are also ancestors of modern starfish and their closest relatives, the acorn worms (the Ambulacraria).<\/p>\n
They have a U-shaped body and were attached to the seafloor with a stalk, with a pair of tentacles on their head used to catch food.<\/p>\n
\u201cThe presence of these ambulacrarians in the Ediacaran period is really exciting,\u201d said Oxford University\u2019s Dr. Frankie Dunn.<\/p>\n
\u201cWe have already found fossils which are distant relatives of starfish and sea cucumbers and are looking for more.\u201d<\/p>\n
\u201cThe discovery of ambulacrarian fossils in the Jiangchuan Biota also means that the chordates \u2014 animals with a backbone \u2014 must also have existed at this time.\u201d<\/p>\n
Other ancestral groups among the fossils include worm-like bilaterian animals, some with complex feeding adaptations, alongside rare fossils interpreted as early comb jellies.<\/p>\n
Many specimens show novel combinations of anatomical features that do not match any known Ediacaran or Cambrian species.<\/p>\n
\u201cOur results indicate that the apparent absence of these complex animal groups from other Ediacaran sites may reflect differences in preservation rather than true biological absence,\u201d said Oxford University\u2019s Dr. Ross Anderson.<\/p>\n
\u201cCarbonaceous compressions like those at Jiangchuan are rare in rocks of this age, meaning that similar communities may simply not have been preserved elsewhere.\u201d<\/p>\n